/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

// Package
///////////////
package org.apache.jena.graph.compose;

import java.util.Iterator ;
import java.util.Set ;

import org.apache.jena.graph.* ;
import org.apache.jena.graph.impl.SimpleEventManager ;
import org.apache.jena.shared.JenaException ;
import org.apache.jena.util.CollectionFactory ;
import org.apache.jena.util.SystemUtils;
import org.apache.jena.util.iterator.ExtendedIterator ;
import org.apache.jena.util.iterator.NullIterator ;

/**
 * <p>
 * A graph implementation that presents the union of zero or more subgraphs,
 * one of which is distinguished as the updateable graph.
 * </p>
 */
public class MultiUnion extends Polyadic
{
    /**
     * <p>
     * Construct a union of exactly no sub graphs.
     * </p>
     */
    public MultiUnion() {
        super();
    }

    /**
     * <p>
     * Construct a union of all of the given graphs
     * </p>
     *
     * @param graphs An array of the sub-graphs of this union
     */
    public MultiUnion( Graph[] graphs) {
        super( graphs );
    }

    /**
     * <p>
     * Construct a union of all of the given graphs.
     * </p>
     *
     * @param graphs An iterator of the sub-graphs of this union. If graphs is
     *               a closable iterator, it will be automatically closed.
     */
    public MultiUnion( Iterator<Graph> graphs ) {
        super( graphs );
    }

    /**
        Answer true iff we're optimising find and query over unions with a
        single element.
    */
    private boolean optimiseOne()
        { return optimising && m_subGraphs.size() == 1; }

    private boolean optimising = SystemUtils.getSystemProperty( "jena.union.optimise", "yes" ).equals( "yes" );

    /**
     * <p>
     * Add the given triple to the union model; the actual component model to
     * be updated will be the designated (or default) {@linkplain #getBaseGraph updateable} graph.
     * </p>
     *
     * @param t A triple to add to the union graph
     * @exception JenaException if the union does not contain any sub-graphs yet
     */
    @Override  public void performAdd( Triple t ) {
        getRequiredBaseGraph().add( t );
    }

    /**
     * <p>
     * Delete the given triple from the union model; the actual component model to
     * be updated will be the designated (or default) {@linkplain #getBaseGraph updateable} graph.
     * </p>
     *
     * @param t A triple to from the union graph
     * @exception JenaException if the union does not contain any sub-graphs yet
     */
    @Override  public void performDelete( Triple t ) {
        getRequiredBaseGraph().delete( t );
    }

    /**
     * <p>
     * Answer true if at least one of the graphs in this union contain the given
     * triple.
     * </p>
     *
     * @param t A triple
     * @return True if any of the graphs in the union contain t
     */
    @Override
    public boolean graphBaseContains(Triple t) {
        for ( Graph m_subGraph : m_subGraphs ) {
            if ( m_subGraph.contains(t) ) {
                return true;
            }
        }
        return false;
    }

    /**
     * <p>
     * Answer an iterator over the triples in the union of the graphs in this composition. <b>Note</b>
     * that the requirement to remove duplicates from the union means that this will be an
     * expensive operation for large (and especially for persistent) graphs.
     * </p>
     *
     * @param t The matcher to match against
     * @return An iterator of all triples matching t in the union of the graphs.
     */
    @Override public ExtendedIterator<Triple> graphBaseFind( final Triple t )
        { // optimise the case where there's only one component graph.
        ExtendedIterator<Triple> found = optimiseOne() ? singleGraphFind( t ) : multiGraphFind( t );
        return SimpleEventManager.notifyingRemove( MultiUnion.this, found );
        }

    /**
         Answer the result of <code>find( t )</code> on the single graph in
         this union.
    */
    private ExtendedIterator<Triple> singleGraphFind(final Triple t) {
        return (m_subGraphs.get(0)).find(t);
    }

    /**
     * Answer the concatenation of all the iterators from a-subGraph.find( t ).
     */
    private ExtendedIterator<Triple> multiGraphFind(final Triple t) {
        Set<Triple> seen = CollectionFactory.createHashedSet();
        ExtendedIterator<Triple> result = NullIterator.instance();
        boolean finished = false;
        try {
            for ( Graph m_subGraph : m_subGraphs ) {
                ExtendedIterator<Triple> newTriples = recording(rejecting(m_subGraph.find(t), seen), seen);
                result = result.andThen(newTriples);
            }
            finished = true;
            return result;
        } finally { // Throwable happened.
            if ( !finished )
                result.close();
        }
    }

    /**
     * <p>
     * Add the given graph to this union.  If it is already a member of the union, don't
     * add it a second time.
     * </p>
     *
     * @param graph A sub-graph to add to this union
     */
    @Override public void addGraph( Graph graph ) {
        if (!m_subGraphs.contains( graph )) {
            m_subGraphs.add( graph );
        }
    }
}
